Inhibitory action of nebracetam on various stimuli-evoked increases in intracellular Ca2+ concentrations in cultured rat cerebellar granule cells

Pyrrolidone derivatives

The pyrrolidone (2-oxopyrrolidine) family of chemicals has been the subject of research for more than three decades. Experimental and clinical work first focused on their so-called nootropic effects; later came the possibilities for neuroprotection after stroke and use as antiepileptic agents. Piracetam, the first of the class, was developed by pioneering research by C Giurgea in the late 1960s, and it was he who coined the term "nootropic", to mean enhancement of learning and memory. The term is sometimes extended to include other actions such as neuroprotection. These properties, together with the lack of other generally adverse psychopharmacological actions (eg, sedation, analgesia, or motor or behavioural changes), distinguish the pyrrolidones from other psychoactive drug classes. The mechanisms of action of these drugs are still not fully established; indeed, different compounds in this class may have different modes of action. Interest in this drug class has recently been reawakened by the licensing of levetiracetam as a potentially major new antiepileptic drug and of piracetam for its antimyoclonic action and effects after stroke and in mild cognitive impairment. Other drugs in this class are currently at an advanced stage of development, and the renewal of interest in this therapeutic area is likely to mean not only that more pyrrolidones will enter clinical practice in the next few years but also that the clinical indications of drugs already licensed will widen.

Inhibition of GABA system involved in cyclosporine-induced convulsions

In this study, we attempted to clarify the mechanisms mediating cyclosporine-evoked convulsions. Cyclosporine (50 mg/kg, i.p.) significantly enhanced the intensity of convulsions induced by bicuculline (GABA receptor antagonist), but not those induced by strychnine (glycine receptor antagonist), N-methyl-D-aspartic acid, quisqualic acid or kainic acid (glutamate receptor agonists). Bicuculline plus cyclosporine-induced convulsions were significantly suppressed by an activation of GABAergic transmission with diazepam, phenobarbital and valproate. The GABA turnover estimated by measuring aminooxyacetic acid-induced GABA accumulation in the mouse brain was significantly inhibited by cyclosporine (50 mg/kg, i.p.). When cultured rat cerebellar granule cells were exposed to 1 microM cyclosporine for 24 hr, the specific [3H]muscimol (10 nM) binding to intact granule cells decreased to 53% of vehicle controls. The present study provides the first evidence suggesting that cyclosporine inhibits GABAergic neural activity and binding properties of the GABAA receptor. These events are closely related to the occurrence of adverse central effects including tremors, convulsions, coma and encephalopathy under cyclosporine therapy.

Age-related changes in the volume of somata and organelles of cerebellar granule cells

Because cerebellar granule cells are fixed post-mitotic cells, it is expected that they undergo age-related changes like other neurons. To examine this possibility, a stereological study on granule cells of rat neocerebellar cortex was performed for an age spectrum of 2 to 24 months using eight different age groups. The nucleator method, together with point and intersection counting, was used to obtain primary data; arithmetical calculations determined the secondary data. In the soma, the absolute surface area did not change significantly; the volume did, however, exhibit a significant negative linear trend with age. Excluding dense bodies, the absolute volumes of the cytoplasmic components did not vary significantly. The absolute volume of dense bodies displayed a significant positive linear trend with age. Significant positive correlations were detected between the somatic volume and the absolute volume of either mitochondria or ground substance. It was concluded that granule cells showed a fair degree of morphological stability through 18 months. However, the observed changes warn that accompanying physiological alterations may occur, with putative effects on motor coordination.